From Wikiexpert

Contents 1 Inline Images 1.1 Problem 1.2 Solution 1.3 Caution

Inline Images

Problem

You want images to show up in your wiki from another site without having to upload the images.

Solution

Inline images are disabled now for security reasons. If you are comfortable with the risk, you can add

$wgAllowExternalImages = true;

to your LocalSettings.php file

Caution

see Copyright. Beware that loading images from a 3rd party site is called bandwidth theft. Your visitor could also be in for nasty surprise